It has become apparent that the earth's natural resources are not unlimited and that mankind's ultimate survival depends on proper conservation of those resources, both by controlling the depletion of raw materials and by eliminating pollution of our land, water and atmosphere. At the same time the world-wide desired for an ever increasing standard of living provides great pressure for rapid production and consumption of goods at the lowest possible immediate cost. Faced with resolving these conflicting demands, planners are increasingly turning to the concept of recycling to provide efficient utilization of raw materials, reduce the output of pollutants and maintain an acceptable supply of goods for our economy.
One material which is a prime candidate for recycling is glass. The non-biodegradable character of glass makes discarded glass a particularly obnoxious pollutant because of its permanency. Glass also is readily subjected to remelting and reforming for reuse.
The principal obstacle in recycling glass is the difficulty of separating glass from other waste materials. The usual route of discarded glass is through municipal waste systems which yield a thoroughly co-mingled mixture of materials of staggering diversity.
Electrostatic separation has been practiced for years primarily in treatment of grains and mineral ores. Actually the use of the term "electrostatic" is a misnomer because most so-called electrostatic separators leak an appreciable current between electrodes and thus are dynamic instead of static in operation. Grains are small and uniform in size. Efficient operation generally required reduction of the ore particles to small size because only very narrow size ranges of low mass particles could be effectively separated. It has been generally thought that high tension separation methods were effective only when the particle sizes of the material being separated were less than about 1/8 inch. Although mineral ores are not usually considered truly homogeneous mixtures, they are much more homogeneous than municipal waste, which incorporates the most diverse types of materials conceivable. Muncipal waste is probably the most heterogeneous mixture known. The very heterogeneous nature of municipal waste coupled with its comparatively low economic value have made it impractical to reduce the waste to particle sizes of the magnitude thought necessary for efficient high tension separation. Thus prior efforts to apply high tension separation techniques to the treatment of municipal waste have not been successful.
I have discovered that the combination of particular electrode configuration and arrangement with special preparation of the municipal waste unexpectedly results in highly efficient separation of glass particles from municipal waste at size ranges well above those previously considered practicable for high tension separation.
It is an object of this invention to provide a method for separating glass particles from municipal waste by high tension means.
It is a further object of this invention to provide a method of the aforesaid character which will efficiently separate particles of larger size than previously processed by high tension methods.
It is an additional object of this invention to provide a method for separating glass from waste material which cn be conveniently added onto existing waste processing treatment facilities with little or no modification to the rest of the ongoing process.
It is also an object of this application to provide a process which will produce a metal free glass cullet product suitable for recycling.
Further objects of the invention will be apparent from a consideration of the specification.